In the process of forming containers by the action of blowing pressure, preforms of a thermoplastic material such as preforms of PET (polyethylene terephthalate) are sent to various processing stations within a blow-molding machine. A blow-molding machine of this type typically comprises a heating device and a blowing device, in the area of which the previously tempered preform is expanded into a container by biaxial orientation. The expansion occurs by means of compressed air, which is introduced into the preform to be expanded. The course of the processing technology involved in a preform expansion of this type is explained in DE-OS 43 40 291. The basic configuration of a blow-molding station for forming containers is described in DE-OS 42 12 583. Possibilities for tempering the preforms are explained in DE-OS 23 52 926.
There are two alternative ways in which the preforms can be sent to the blow-molding machine. In the case of the so-called “one-step” method, the preforms are produced by an injection-molding process, and, immediately after they have been injection-molded, they are transported directly to the blow-molding machine by a conveying apparatus. In the case of the so-called “two-step” method, the preforms are first produced by an injection-molding process and then stored; they are conditioned with respect to their temperature and then blown into containers only at a later time. The production of the preforms and the blow-molding of the preforms into containers can take place at different times and at different places.
Both methods have in common that the preforms are sent the blow-molding machine by a conveying apparatus. Known apparatuses consist of, for example, a vertical conveyor, by which the preforms, which are stored in a collecting bin, are transported to a conveying device. By means of the conveying device, usually a conveyor belt, the preforms are transported to a sorting device. This sorting device has the task of orienting the preforms into a defined position so that they can be transferred to, for example, a downline blow-molding machine. Known sorting devices (so-called roll sorters) consist, for example, of two conveying rolls, which rotate in opposite directions and between which a small gap remains, which is selected in such a way that the preforms can be held, suspended by their collars, between the rotating conveying rolls. The conveying rolls are arranged at an angle, so that the preforms slide down the incline, i.e., in the conveying direction, along the conveying rolls. In this way the preforms are sorted, suspended between the rotating rolls, and then conveyed in the conveying direction to, for example, the blow-molding machine. As a rule, the conveying device upstream of the sorting device is arranged in such a way that that the preforms drop onto the sorting device upon reaching the end of the conveying device, e.g., by gravity from the end of the conveyor belt. To prevent the preforms from bouncing back out of the sorting device when they land, a feed device is usually provided between the conveying device and the sorting device. This feed device is configured so that it surrounds the transfer one between the conveying device and the sorting device, so that the falling and bouncing preforms strike the side walls of the feed device and then fall back down into the sorting device. The task of the feed device is to facilitate the sorting of the preforms.
Deflecting devices are also usually provided in the feed device. These deflecting devices can be in the form of slide plates, for example, by means of which the speed at which the preforms are dropping can be reduced, as a result of which the bouncing of the preforms is decreased.
In the known feed devices, the deflecting devices are arranged in such a way that some of the falling preforms are guided along the deflecting device in a direction opposite to the conveying direction of the preforms in the sorting device (“the conveying direction” below), either dropping straight down into the sorting device or sideways, transversely to the conveying direction. This orientation has the result that the speed of the preforms as they land on the sorting unit decreases to practically zero. Then the preforms are conveyed further along and oriented by the conveying aids provided in the sorting unit.
The disadvantage of this known apparatus is that the flow rate of the preforms can be increased only up to a certain throughput. A throughput beyond this point, such as that required for high-performance blow-molding machines, for example, is not possible with the known apparatuses. The conveying performance of smaller systems, furthermore, can be increased.